16 mark
Explain the
major levels of embedded system design process with an example. (16)
ANS :
ü A
procedure for designing a system.
ü Understanding
your methodology helps you ensure you didn’t skip anything.
ü Compilers,
software engineering tools, computer-aided design (CAD) tools, etc., can be
used to:
-
help automate methodology steps;
-
keep track of the methodology itself.
Ø Design goals
ü Performance.
-
Overall speed, deadlines.
ü Functionality
and user interface.
ü Manufacturing
cost.
ü Power
consumption.
ü Other
requirements (physical size, etc.)
Ø Levels of abstraction
Ø Top-down vs. bottom-up
ü Top-down
design:
-
start from most abstract description;
-
work to most detailed.
ü Bottom-up
design:
-
work from small components to big system.
ü Real
design uses both techniques.
Ø Stepwise refinement
ü At each
level of abstraction, we must:
-
analyze the design to determine characteristics
of the current state of the design;
-
refine the design to add detail.
Ø Requirements
ü Plain
language description of what the user wants and expects to get.
ü May be
developed in several ways:
-
talking directly to customers;
-
talking to marketing representatives;
-
providing prototypes to users for comment.
Ø Functional vs. non-functional requirements
ü Functional
requirements:
-
output as a function of input.
ü Non-functional
requirements:
-
time required to compute output;
-
size, weight, etc.;
-
power consumption;
-
reliability;.
Ø Typical nonfunctional requirements include:
ü Performance: The
speed of the system is often a major consideration both for the usability of
the system and for its ultimate cost. As we have noted, performance may be a
combination of soft performance metrics such as approximate time to perform a
user-level function and hard deadlines by which a particular operation must be
completed.
ü Cost: The target
cost or purchase price for the system is almost always a consideration. Cost
typically has two major components: manufacturing cost includes
the cost of components and assembly; nonrecurring engineering (NRE) costs
include the personnel and other costs of designing the system.
ü Physical size and weight: The
physical aspects of the final system can vary greatly depending upon the
application. An industrial control system for an assembly line may be designed
to fit into a standard-size rack with no strict limitations on weight. A
handheld device typically has tight requirements on both size and weight that
can ripple through the entire system design.
ü Power consumption: Power,
of course, is important in battery-powered systems and is often important in other
applications as well. Power can be specified in the requirements stage in terms
of battery life—the customer is unlikely to be able to describe the allowable
wattage.
Ø Our
sample requirements form
|
inputs
|
|
outputs
|
|
functions
|
|
performance
|
|
manufacturing cost
|
|
power
|
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physical size/weight
|
Example:
GPS moving map requirements
ü Moving
map obtains position from GPS, paints map from local database.
GPS
moving map needs
ü Functionality:
For automotive use. Show major roads and landmarks.
ü User
interface: At least 400 x 600 pixel screen. Three buttons max. Pop-up menu.
ü Performance:
Map should scroll smoothly. No more than 1 sec power-up. Lock onto GPS within
15 seconds.
ü Cost:
$120 street price = approx. $30 cost of goods sold.
ü Physical
size/weight: Should fit in hand.
ü Power
consumption: Should run for 8 hours on four AA batteries.
GPS
moving map requirements form
|
name
|
GPS moving map
|
|
purpose
|
consumer-grade moving map for driving
|
|
inputs
|
power button, two control buttons
|
|
outputs
|
back-lit LCD 400 X 600
|
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functions
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5-receiver GPS; three resolutions; displays current lat/lon
|
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performance
|
updates screen within 0.25 sec of movement
|
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manufacturing cost
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$100 cost-of-goods-sold
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power
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100 mW
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physical size/weight
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no more than 2: X 6:, 12 oz.
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|
|
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Ø Specification
ü A more
precise description of the system:
-
should not imply a particular architecture;
-
provides input to the architecture design
process.
ü May
include functional and non-functional elements.
ü May be
executable or may be in mathematical form for proofs.
GPS specification
ü Should
include:
-
What is received from GPS;
-
map data;
-
user interface;
-
operations required to satisfy user requests;
-
background operations needed to keep the system
running.
Architecture
design
ü What
major components go satisfying the specification?
ü Hardware
components:
-
CPUs, peripherals, etc.
ü Software
components:
-
major programs and their operations.
ü Must
take into account functional and non-functional specifications.
Ø Designing hardware and software components
ü Must
spend time architecting the system before you start coding.
ü Some
components are ready-made, some can be
modified from existing designs, others must be designed from scratch.
System
integration
ü Put
together the components.
-
Many bugs appear only at this stage.
ü Have a
plan for integrating components to uncover bugs quickly, test as much
functionality as early as possible.
Summary
ü Embedded
computers are all around us.
-
Many systems have complex embedded hardware and
software.
ü Embedded
systems pose many design challenges: design time, deadlines, power, etc.
Design methodologies help us manage the design process
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